Loose nukes: Would earthquakes around Yucca Mountain make it unsafe to hold nuclear waste?

The generation-long debate surrounding the dumping of the nation’s radioactive nuclear waste under Nevada’s Yucca Mountain may finally be drawing to a close. As ScientificAmerican.com reported yesterday, the plan to turn the mountain – some 100 miles (160 kilometers) from Las Vegas – into a nuclear repository appears to be dead in the water: President Obama’s proposed 2010 budget removes major funding needed to complete the project – and it faces opposition from powerful Senate Majority Leader Harry Reid, a Nevada Democrat, who doesn't want the country's spent nuclear fuel dumped in his state.

Critics of the plan charge, among other things, that the site might not be the securest of spots to store radioactive materials given the potential of earthquakes in the area. After all, they note, Nevada is the third-most seismically active state in the U.S.

But is there really cause for concern?

"There is an earthquake hazard around Yucca Mountain that’s greater than, say, the northeastern United States, but much less than that faced by Los Angeles or San Francisco," says John Anderson, director of the Nevada Seismological Lab (NSL) based at the University of Nevada, Reno. The lab has monitored the Yucca Mountain region since 1992 when it received a grant from the Department of Energy (DOE) to help ascertain the site’s suitability as a nuclear waste graveyard.

The hazard of earthquakes stems from faults that scientists have detected around Yucca Mountain, Anderson says. Faults are fractures in the Earth’s rocky crust that allow movement between two masses of stone. When this slippage happens abruptly, presto, you’ve got an earthquake. Typically the longer a fault, the more earthquake potential it carries. For example, the infamous San Andreas fault that can produce devastating earthquakes of magnitude eight or nine on the Richter scale runs about 800 miles (1300 kilometers) under much of California's western shoreline.

The tectonics in southern Nevada where Yucca Mountain is located pale in comparison. “Hazard analyses of the faults close to Yucca Mountain indicate they could not produce more than a seven [on the Richter scale],” says Anderson. A seven can still do significant damage and qualifies as a major earthquake, though such a quake falls far short of, say, the apocalyptic magnitude 9.1 to 9.3 that triggered the Asian tsunami in 2004.

Tiny quakes near Yucca Mountain often shake things up a bit, however: NSL records about 10 micro-earthquakes of less than magnitude two or so daily within a 30 mile (50 kilometer) range of the once-slated nuclear repository, according to the lab’s website. Though it may look more alarming than it really is, check out this map (PDF) peppered with circles representing earthquakes recorded between 1992 and 2006 around Yucca Mountain by the NSL.

The only sizable quake that shook the region in recent history registered a magnitude 5.7, substantially damaging DOE buildings in the vicinity but not the fledging facilities at Yucca back in 1992. People who have worked in the Yucca environs, including at the Nevada Test Site in the desert at the mountain’s edge (where the U.S. detonated over 900 nuclear weapons above and below ground from 1951 to 1992), have reported feeling non-manmade tremors as well.

The DOE says this frequent, if low-level, seismic activity does not pose a threat to potential safe nuclear storage some five miles (eight kilometers) under Yucca Mountain. The DOE says on its Yucca Mountain web page (which remains the same as it was pre-President Obama and his Energy Secretary Steven Chu, who both oppose it as a nuke repository) in a posting that's been there since 2003:

"Experience with earthquakes throughout the world has shown that underground structures can withstand the ground motion generated by earthquakes. And, in actual tests at the Nevada Test Site mine tunnels have withstood ground motion from underground nuclear explosions that are greater than any ground motion anticipated at or near Yucca Mountain. Repository facilities at the surface also can be designed to safely withstand earthquake effects."

In other words, the proposed Yucca Mountain repository could withstand whatever earthquakes Mother Nature might muster – except, perhaps, the shifting of the political ground.

Yucca Mountain, Nevada. Image Credit: USGS

The views expressed are those of the author and are not necessarily those of Scientific American.

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